Rollup merge of #61606 - petrochenkov:legclean, r=pnkfelix

Remove some legacy proc macro flavors

Namely
- `IdentTT` (`foo! ident { ... }`). Can be replaced with `foo! { ident ... }` or something similar.
- `MultiDecorator`. Can be replaced by `MultiModifier` (aka `LegacyAttr` after renaming).
- `DeclMacro`. It was a less powerful duplicate of `NormalTT` (aka `LegacyBang` after renaming) and can be replaced by it.

Stuff like this slows down any attempts to refactor the expansion infra, so it's desirable to retire it already.
I'm not sure whether a lang team decision is necessary, but would be nice to land this sooner because I have some further work in this area scheduled.

The documentation commit (https://github.com/rust-lang/rust/commit/a9397fd0d5eede4bbc0ada94bf92657ca8084cb3) describes how the remaining variants are different from each other and shows that there's actually some system behind them.

The last commit renames variants of `SyntaxExtension` in more systematic way.
- `ProcMacro` -> `Bang`
- `NormalTT` -> `LegacyBang`
- `AttrProcMacro` -> `Attr`
- `MultiModifier` -> `LegacyAttr`
- `ProcMacroDerive` -> `Derive`
- `BuiltinDerive` -> `LegacyDerive`

All the `Legacy*` variants are AST-based, as opposed to "modern" token-based variants.

3 files changed, 166 insertions, 273 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 61c736662c7..38b7dee40c4 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -1,6 +1,4 @@
-pub use SyntaxExtension::*;
-
-use crate::ast::{self, Attribute, Name, PatKind, MetaItem};
+use crate::ast::{self, Attribute, Name, PatKind};
 use crate::attr::HasAttrs;
 use crate::source_map::{SourceMap, Spanned, respan};
 use crate::edition::Edition;
@@ -137,29 +135,6 @@ impl Annotatable {
     }
 }
 
-// A more flexible ItemDecorator.
-pub trait MultiItemDecorator {
-    fn expand(&self,
-              ecx: &mut ExtCtxt<'_>,
-              sp: Span,
-              meta_item: &ast::MetaItem,
-              item: &Annotatable,
-              push: &mut dyn FnMut(Annotatable));
-}
-
-impl<F> MultiItemDecorator for F
-    where F : Fn(&mut ExtCtxt<'_>, Span, &ast::MetaItem, &Annotatable, &mut dyn FnMut(Annotatable))
-{
-    fn expand(&self,
-              ecx: &mut ExtCtxt<'_>,
-              sp: Span,
-              meta_item: &ast::MetaItem,
-              item: &Annotatable,
-              push: &mut dyn FnMut(Annotatable)) {
-        (*self)(ecx, sp, meta_item, item, push)
-    }
-}
-
 // `meta_item` is the annotation, and `item` is the item being modified.
 // FIXME Decorators should follow the same pattern too.
 pub trait MultiItemModifier {
@@ -288,34 +263,6 @@ impl<F> TTMacroExpander for F
     }
 }
 
-pub trait IdentMacroExpander {
-    fn expand<'cx>(&self,
-                   cx: &'cx mut ExtCtxt<'_>,
-                   sp: Span,
-                   ident: ast::Ident,
-                   token_tree: Vec<tokenstream::TokenTree>)
-                   -> Box<dyn MacResult+'cx>;
-}
-
-pub type IdentMacroExpanderFn =
-    for<'cx> fn(&'cx mut ExtCtxt<'_>, Span, ast::Ident, Vec<tokenstream::TokenTree>)
-                -> Box<dyn MacResult+'cx>;
-
-impl<F> IdentMacroExpander for F
-    where F : for<'cx> Fn(&'cx mut ExtCtxt<'_>, Span, ast::Ident,
-                          Vec<tokenstream::TokenTree>) -> Box<dyn MacResult+'cx>
-{
-    fn expand<'cx>(&self,
-                   cx: &'cx mut ExtCtxt<'_>,
-                   sp: Span,
-                   ident: ast::Ident,
-                   token_tree: Vec<tokenstream::TokenTree>)
-                   -> Box<dyn MacResult+'cx>
-    {
-        (*self)(cx, sp, ident, token_tree)
-    }
-}
-
 // Use a macro because forwarding to a simple function has type system issues
 macro_rules! make_stmts_default {
     ($me:expr) => {
@@ -570,9 +517,6 @@ impl MacResult for DummyResult {
     }
 }
 
-pub type BuiltinDeriveFn =
-    for<'cx> fn(&'cx mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable));
-
 /// Represents different kinds of macro invocations that can be resolved.
 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum MacroKind {
@@ -606,129 +550,116 @@ impl MacroKind {
 
 /// An enum representing the different kinds of syntax extensions.
 pub enum SyntaxExtension {
-    /// A trivial "extension" that does nothing, only keeps the attribute and marks it as known.
-    NonMacroAttr { mark_used: bool },
-
-    /// A syntax extension that is attached to an item and creates new items
-    /// based upon it.
-    ///
-    /// `#[derive(...)]` is a `MultiItemDecorator`.
-    ///
-    /// Prefer ProcMacro or MultiModifier since they are more flexible.
-    MultiDecorator(Box<dyn MultiItemDecorator + sync::Sync + sync::Send>),
-
-    /// A syntax extension that is attached to an item and modifies it
-    /// in-place. Also allows decoration, i.e., creating new items.
-    MultiModifier(Box<dyn MultiItemModifier + sync::Sync + sync::Send>),
-
-    /// A function-like procedural macro. TokenStream -> TokenStream.
-    ProcMacro {
+    /// A token-based function-like macro.
+    Bang {
+        /// An expander with signature TokenStream -> TokenStream.
         expander: Box<dyn ProcMacro + sync::Sync + sync::Send>,
-        /// Whitelist of unstable features that are treated as stable inside this macro
+        /// Whitelist of unstable features that are treated as stable inside this macro.
         allow_internal_unstable: Option<Lrc<[Symbol]>>,
+        /// Edition of the crate in which this macro is defined.
         edition: Edition,
     },
 
-    /// An attribute-like procedural macro. TokenStream, TokenStream -> TokenStream.
-    /// The first TokenSteam is the attribute, the second is the annotated item.
-    /// Allows modification of the input items and adding new items, similar to
-    /// MultiModifier, but uses TokenStreams, rather than AST nodes.
-    AttrProcMacro(Box<dyn AttrProcMacro + sync::Sync + sync::Send>, Edition),
-
-    /// A normal, function-like syntax extension.
-    ///
-    /// `bytes!` is a `NormalTT`.
-    NormalTT {
+    /// An AST-based function-like macro.
+    LegacyBang {
+        /// An expander with signature TokenStream -> AST.
         expander: Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
+        /// Some info about the macro's definition point.
         def_info: Option<(ast::NodeId, Span)>,
-        /// Whether the contents of the macro can
-        /// directly use `#[unstable]` things.
-        ///
-        /// Only allows things that require a feature gate in the given whitelist
+        /// Hygienic properties of identifiers produced by this macro.
+        transparency: Transparency,
+        /// Whitelist of unstable features that are treated as stable inside this macro.
         allow_internal_unstable: Option<Lrc<[Symbol]>>,
-        /// Whether the contents of the macro can use `unsafe`
-        /// without triggering the `unsafe_code` lint.
+        /// Suppresses the `unsafe_code` lint for code produced by this macro.
         allow_internal_unsafe: bool,
-        /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
-        /// for a given macro.
+        /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`) for this macro.
         local_inner_macros: bool,
-        /// The macro's feature name if it is unstable, and the stability feature
+        /// The macro's feature name and tracking issue number if it is unstable.
         unstable_feature: Option<(Symbol, u32)>,
-        /// Edition of the crate in which the macro is defined
+        /// Edition of the crate in which this macro is defined.
         edition: Edition,
     },
 
-    /// A function-like syntax extension that has an extra ident before
-    /// the block.
-    IdentTT {
-        expander: Box<dyn IdentMacroExpander + sync::Sync + sync::Send>,
-        span: Option<Span>,
-        allow_internal_unstable: Option<Lrc<[Symbol]>>,
+    /// A token-based attribute macro.
+    Attr(
+        /// An expander with signature (TokenStream, TokenStream) -> TokenStream.
+        /// The first TokenSteam is the attribute itself, the second is the annotated item.
+        /// The produced TokenSteam replaces the input TokenSteam.
+        Box<dyn AttrProcMacro + sync::Sync + sync::Send>,
+        /// Edition of the crate in which this macro is defined.
+        Edition,
+    ),
+
+    /// An AST-based attribute macro.
+    LegacyAttr(
+        /// An expander with signature (AST, AST) -> AST.
+        /// The first AST fragment is the attribute itself, the second is the annotated item.
+        /// The produced AST fragment replaces the input AST fragment.
+        Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
+    ),
+
+    /// A trivial attribute "macro" that does nothing,
+    /// only keeps the attribute and marks it as known.
+    NonMacroAttr {
+        /// Suppresses the `unused_attributes` lint for this attribute.
+        mark_used: bool,
     },
 
-    /// An attribute-like procedural macro. TokenStream -> TokenStream.
-    /// The input is the annotated item.
-    /// Allows generating code to implement a Trait for a given struct
-    /// or enum item.
-    ProcMacroDerive(Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
-                    Vec<Symbol> /* inert attribute names */, Edition),
-
-    /// An attribute-like procedural macro that derives a builtin trait.
-    BuiltinDerive(BuiltinDeriveFn),
-
-    /// A declarative macro, e.g., `macro m() {}`.
-    DeclMacro {
-        expander: Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
-        def_info: Option<(ast::NodeId, Span)>,
-        is_transparent: bool,
-        edition: Edition,
-    }
+    /// A token-based derive macro.
+    Derive(
+        /// An expander with signature TokenStream -> TokenStream (not yet).
+        /// The produced TokenSteam is appended to the input TokenSteam.
+        Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
+        /// Names of helper attributes registered by this macro.
+        Vec<Symbol>,
+        /// Edition of the crate in which this macro is defined.
+        Edition,
+    ),
+
+    /// An AST-based derive macro.
+    LegacyDerive(
+        /// An expander with signature AST -> AST.
+        /// The produced AST fragment is appended to the input AST fragment.
+        Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
+    ),
 }
 
 impl SyntaxExtension {
     /// Returns which kind of macro calls this syntax extension.
     pub fn kind(&self) -> MacroKind {
         match *self {
-            SyntaxExtension::DeclMacro { .. } |
-            SyntaxExtension::NormalTT { .. } |
-            SyntaxExtension::IdentTT { .. } |
-            SyntaxExtension::ProcMacro { .. } =>
-                MacroKind::Bang,
-            SyntaxExtension::NonMacroAttr { .. } |
-            SyntaxExtension::MultiDecorator(..) |
-            SyntaxExtension::MultiModifier(..) |
-            SyntaxExtension::AttrProcMacro(..) =>
-                MacroKind::Attr,
-            SyntaxExtension::ProcMacroDerive(..) |
-            SyntaxExtension::BuiltinDerive(..) =>
-                MacroKind::Derive,
+            SyntaxExtension::Bang { .. } |
+            SyntaxExtension::LegacyBang { .. } => MacroKind::Bang,
+            SyntaxExtension::Attr(..) |
+            SyntaxExtension::LegacyAttr(..) |
+            SyntaxExtension::NonMacroAttr { .. } => MacroKind::Attr,
+            SyntaxExtension::Derive(..) |
+            SyntaxExtension::LegacyDerive(..) => MacroKind::Derive,
         }
     }
 
     pub fn default_transparency(&self) -> Transparency {
         match *self {
-            SyntaxExtension::ProcMacro { .. } |
-            SyntaxExtension::AttrProcMacro(..) |
-            SyntaxExtension::ProcMacroDerive(..) |
-            SyntaxExtension::DeclMacro { is_transparent: false, .. } => Transparency::Opaque,
-            SyntaxExtension::DeclMacro { is_transparent: true, .. } => Transparency::Transparent,
-            _ => Transparency::SemiTransparent,
+            SyntaxExtension::LegacyBang { transparency, .. } => transparency,
+            SyntaxExtension::Bang { .. } |
+            SyntaxExtension::Attr(..) |
+            SyntaxExtension::Derive(..) |
+            SyntaxExtension::NonMacroAttr { .. } => Transparency::Opaque,
+            SyntaxExtension::LegacyAttr(..) |
+            SyntaxExtension::LegacyDerive(..) => Transparency::SemiTransparent,
         }
     }
 
     pub fn edition(&self, default_edition: Edition) -> Edition {
         match *self {
-            SyntaxExtension::NormalTT { edition, .. } |
-            SyntaxExtension::DeclMacro { edition, .. } |
-            SyntaxExtension::ProcMacro { edition, .. } |
-            SyntaxExtension::AttrProcMacro(.., edition) |
-            SyntaxExtension::ProcMacroDerive(.., edition) => edition,
+            SyntaxExtension::Bang { edition, .. } |
+            SyntaxExtension::LegacyBang { edition, .. } |
+            SyntaxExtension::Attr(.., edition) |
+            SyntaxExtension::Derive(.., edition) => edition,
             // Unstable legacy stuff
             SyntaxExtension::NonMacroAttr { .. } |
-            SyntaxExtension::IdentTT { .. } |
-            SyntaxExtension::MultiDecorator(..) |
-            SyntaxExtension::MultiModifier(..) |
-            SyntaxExtension::BuiltinDerive(..) => default_edition,
+            SyntaxExtension::LegacyAttr(..) |
+            SyntaxExtension::LegacyDerive(..) => default_edition,
         }
     }
 }
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 99605395553..084d4fd3820 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -389,7 +389,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         let item = match self.cx.resolver.resolve_macro_path(
                                 path, MacroKind::Derive, Mark::root(), Vec::new(), false) {
                             Ok(ext) => match *ext {
-                                BuiltinDerive(..) => item_with_markers.clone(),
+                                SyntaxExtension::LegacyDerive(..) => item_with_markers.clone(),
                                 _ => item.clone(),
                             },
                             _ => item.clone(),
@@ -548,7 +548,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             _ => unreachable!(),
         };
 
-        if let NonMacroAttr { mark_used: false } = *ext {} else {
+        if let SyntaxExtension::NonMacroAttr { mark_used: false } = *ext {} else {
             // Macro attrs are always used when expanded,
             // non-macro attrs are considered used when the field says so.
             attr::mark_used(&attr);
@@ -564,26 +564,18 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         });
 
         match *ext {
-            NonMacroAttr { .. } => {
+            SyntaxExtension::NonMacroAttr { .. } => {
                 attr::mark_known(&attr);
                 item.visit_attrs(|attrs| attrs.push(attr));
                 Some(invoc.fragment_kind.expect_from_annotatables(iter::once(item)))
             }
-            MultiModifier(ref mac) => {
+            SyntaxExtension::LegacyAttr(ref mac) => {
                 let meta = attr.parse_meta(self.cx.parse_sess)
                                .map_err(|mut e| { e.emit(); }).ok()?;
                 let item = mac.expand(self.cx, attr.span, &meta, item);
                 Some(invoc.fragment_kind.expect_from_annotatables(item))
             }
-            MultiDecorator(ref mac) => {
-                let mut items = Vec::new();
-                let meta = attr.parse_meta(self.cx.parse_sess)
-                               .expect("derive meta should already have been parsed");
-                mac.expand(self.cx, attr.span, &meta, &item, &mut |item| items.push(item));
-                items.push(item);
-                Some(invoc.fragment_kind.expect_from_annotatables(items))
-            }
-            AttrProcMacro(ref mac, ..) => {
+            SyntaxExtension::Attr(ref mac, ..) => {
                 self.gate_proc_macro_attr_item(attr.span, &item);
                 let item_tok = TokenTree::token(token::Interpolated(Lrc::new(match item {
                     Annotatable::Item(item) => token::NtItem(item),
@@ -600,7 +592,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 self.gate_proc_macro_expansion(attr.span, &res);
                 res
             }
-            ProcMacroDerive(..) | BuiltinDerive(..) => {
+            SyntaxExtension::Derive(..) | SyntaxExtension::LegacyDerive(..) => {
                 self.cx.span_err(attr.span, &format!("`{}` is a derive macro", attr.path));
                 self.cx.trace_macros_diag();
                 invoc.fragment_kind.dummy(attr.span)
@@ -755,17 +747,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         };
 
         let opt_expanded = match *ext {
-            DeclMacro { ref expander, def_info, edition, .. } => {
-                if let Err(dummy_span) = validate_and_set_expn_info(self, def_info.map(|(_, s)| s),
-                                                                    None, false, false, None,
-                                                                    edition) {
-                    dummy_span
-                } else {
-                    kind.make_from(expander.expand(self.cx, span, mac.node.stream(), None))
-                }
-            }
-
-            NormalTT {
+            SyntaxExtension::LegacyBang {
                 ref expander,
                 def_info,
                 ref allow_internal_unstable,
@@ -773,6 +755,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 local_inner_macros,
                 unstable_feature,
                 edition,
+                ..
             } => {
                 if let Err(dummy_span) = validate_and_set_expn_info(self, def_info.map(|(_, s)| s),
                                                                     allow_internal_unstable.clone(),
@@ -791,43 +774,22 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 }
             }
 
-            IdentTT { ref expander, span: tt_span, ref allow_internal_unstable } => {
-                if ident.name == kw::Invalid {
-                    self.cx.span_err(path.span,
-                                    &format!("macro {}! expects an ident argument", path));
-                    self.cx.trace_macros_diag();
-                    kind.dummy(span)
-                } else {
-                    invoc.expansion_data.mark.set_expn_info(ExpnInfo {
-                        call_site: span,
-                        def_site: tt_span,
-                        format: macro_bang_format(path),
-                        allow_internal_unstable: allow_internal_unstable.clone(),
-                        allow_internal_unsafe: false,
-                        local_inner_macros: false,
-                        edition: self.cx.parse_sess.edition,
-                    });
-
-                    let input: Vec<_> = mac.node.stream().into_trees().collect();
-                    kind.make_from(expander.expand(self.cx, span, ident, input))
-                }
-            }
-
-            MultiDecorator(..) | MultiModifier(..) |
-            AttrProcMacro(..) | SyntaxExtension::NonMacroAttr { .. } => {
+            SyntaxExtension::Attr(..) |
+            SyntaxExtension::LegacyAttr(..) |
+            SyntaxExtension::NonMacroAttr { .. } => {
                 self.cx.span_err(path.span,
                                  &format!("`{}` can only be used in attributes", path));
                 self.cx.trace_macros_diag();
                 kind.dummy(span)
             }
 
-            ProcMacroDerive(..) | BuiltinDerive(..) => {
+            SyntaxExtension::Derive(..) | SyntaxExtension::LegacyDerive(..) => {
                 self.cx.span_err(path.span, &format!("`{}` is a derive macro", path));
                 self.cx.trace_macros_diag();
                 kind.dummy(span)
             }
 
-            SyntaxExtension::ProcMacro { ref expander, ref allow_internal_unstable, edition } => {
+            SyntaxExtension::Bang { ref expander, ref allow_internal_unstable, edition } => {
                 if ident.name != kw::Invalid {
                     let msg =
                         format!("macro {}! expects no ident argument, given '{}'", path, ident);
@@ -924,29 +886,29 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             edition: ext.edition(self.cx.parse_sess.edition),
         };
 
-        match *ext {
-            ProcMacroDerive(ref ext, ..) => {
-                invoc.expansion_data.mark.set_expn_info(expn_info);
-                let span = span.with_ctxt(self.cx.backtrace());
-                let dummy = ast::MetaItem { // FIXME(jseyfried) avoid this
-                    path: Path::from_ident(Ident::invalid()),
-                    span: DUMMY_SP,
-                    node: ast::MetaItemKind::Word,
+        match ext {
+            SyntaxExtension::Derive(expander, ..) | SyntaxExtension::LegacyDerive(expander) => {
+                let meta = match ext {
+                    SyntaxExtension::Derive(..) => ast::MetaItem { // FIXME(jseyfried) avoid this
+                        path: Path::from_ident(Ident::invalid()),
+                        span: DUMMY_SP,
+                        node: ast::MetaItemKind::Word,
+                    },
+                    _ => {
+                        expn_info.allow_internal_unstable = Some(vec![
+                            sym::rustc_attrs,
+                            Symbol::intern("derive_clone_copy"),
+                            Symbol::intern("derive_eq"),
+                            // RustcDeserialize and RustcSerialize
+                            Symbol::intern("libstd_sys_internals"),
+                        ].into());
+                        attr.meta()?
+                    }
                 };
-                let items = ext.expand(self.cx, span, &dummy, item);
-                Some(invoc.fragment_kind.expect_from_annotatables(items))
-            }
-            BuiltinDerive(func) => {
-                expn_info.allow_internal_unstable = Some(vec![
-                    sym::rustc_attrs,
-                    Symbol::intern("derive_clone_copy"),
-                    Symbol::intern("derive_eq"),
-                    Symbol::intern("libstd_sys_internals"), // RustcDeserialize and RustcSerialize
-                ].into());
+
                 invoc.expansion_data.mark.set_expn_info(expn_info);
                 let span = span.with_ctxt(self.cx.backtrace());
-                let mut items = Vec::new();
-                func(self.cx, span, &attr.meta()?, &item, &mut |a| items.push(a));
+                let items = expander.expand(self.cx, span, &meta, item);
                 Some(invoc.fragment_kind.expect_from_annotatables(items))
             }
             _ => {
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 6f82f509465..5dbf21867af 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -1,8 +1,8 @@
 use crate::{ast, attr};
 use crate::edition::Edition;
-use crate::ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension};
-use crate::ext::base::{NormalTT, TTMacroExpander};
+use crate::ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension, TTMacroExpander};
 use crate::ext::expand::{AstFragment, AstFragmentKind};
+use crate::ext::hygiene::Transparency;
 use crate::ext::tt::macro_parser::{Success, Error, Failure};
 use crate::ext::tt::macro_parser::{MatchedSeq, MatchedNonterminal};
 use crate::ext::tt::macro_parser::{parse, parse_failure_msg};
@@ -374,65 +374,65 @@ pub fn compile(
         valid,
     });
 
-    if body.legacy {
-        let allow_internal_unstable = attr::find_by_name(&def.attrs, sym::allow_internal_unstable)
-            .map(|attr| attr
-                .meta_item_list()
-                .map(|list| list.iter()
-                    .filter_map(|it| {
-                        let name = it.ident().map(|ident| ident.name);
-                        if name.is_none() {
-                            sess.span_diagnostic.span_err(it.span(),
-                                "allow internal unstable expects feature names")
-                        }
-                        name
-                    })
-                    .collect::<Vec<Symbol>>().into()
-                )
-                .unwrap_or_else(|| {
-                    sess.span_diagnostic.span_warn(
-                        attr.span, "allow_internal_unstable expects list of feature names. In the \
-                        future this will become a hard error. Please use `allow_internal_unstable(\
-                        foo, bar)` to only allow the `foo` and `bar` features",
-                    );
-                    vec![sym::allow_internal_unstable_backcompat_hack].into()
+    let transparency = if attr::contains_name(&def.attrs, sym::rustc_transparent_macro) {
+        Transparency::Transparent
+    } else if body.legacy {
+        Transparency::SemiTransparent
+    } else {
+        Transparency::Opaque
+    };
+
+    let allow_internal_unstable = attr::find_by_name(&def.attrs, sym::allow_internal_unstable)
+        .map(|attr| attr
+            .meta_item_list()
+            .map(|list| list.iter()
+                .filter_map(|it| {
+                    let name = it.ident().map(|ident| ident.name);
+                    if name.is_none() {
+                        sess.span_diagnostic.span_err(it.span(),
+                            "allow internal unstable expects feature names")
+                    }
+                    name
                 })
-            );
-        let allow_internal_unsafe = attr::contains_name(&def.attrs, sym::allow_internal_unsafe);
-        let mut local_inner_macros = false;
-        if let Some(macro_export) = attr::find_by_name(&def.attrs, sym::macro_export) {
-            if let Some(l) = macro_export.meta_item_list() {
-                local_inner_macros = attr::list_contains_name(&l, sym::local_inner_macros);
-            }
-        }
+                .collect::<Vec<Symbol>>().into()
+            )
+            .unwrap_or_else(|| {
+                sess.span_diagnostic.span_warn(
+                    attr.span, "allow_internal_unstable expects list of feature names. In the \
+                    future this will become a hard error. Please use `allow_internal_unstable(\
+                    foo, bar)` to only allow the `foo` and `bar` features",
+                );
+                vec![sym::allow_internal_unstable_backcompat_hack].into()
+            })
+        );
 
-        let unstable_feature = attr::find_stability(&sess,
-                                                    &def.attrs, def.span).and_then(|stability| {
-            if let attr::StabilityLevel::Unstable { issue, .. } = stability.level {
-                Some((stability.feature, issue))
-            } else {
-                None
-            }
-        });
-
-        NormalTT {
-            expander,
-            def_info: Some((def.id, def.span)),
-            allow_internal_unstable,
-            allow_internal_unsafe,
-            local_inner_macros,
-            unstable_feature,
-            edition,
+    let allow_internal_unsafe = attr::contains_name(&def.attrs, sym::allow_internal_unsafe);
+
+    let mut local_inner_macros = false;
+    if let Some(macro_export) = attr::find_by_name(&def.attrs, sym::macro_export) {
+        if let Some(l) = macro_export.meta_item_list() {
+            local_inner_macros = attr::list_contains_name(&l, sym::local_inner_macros);
         }
-    } else {
-        let is_transparent = attr::contains_name(&def.attrs, sym::rustc_transparent_macro);
+    }
 
-        SyntaxExtension::DeclMacro {
-            expander,
-            def_info: Some((def.id, def.span)),
-            is_transparent,
-            edition,
+    let unstable_feature = attr::find_stability(&sess,
+                                                &def.attrs, def.span).and_then(|stability| {
+        if let attr::StabilityLevel::Unstable { issue, .. } = stability.level {
+            Some((stability.feature, issue))
+        } else {
+            None
         }
+    });
+
+    SyntaxExtension::LegacyBang {
+        expander,
+        def_info: Some((def.id, def.span)),
+        transparency,
+        allow_internal_unstable,
+        allow_internal_unsafe,
+        local_inner_macros,
+        unstable_feature,
+        edition,
     }
 }